The title compound, {[Fe(NCSe)2(C12H12N2)(H2O)2]·2C12H12N2·2H2O}n, was obtained by the reaction of iron(II) sulfate heptahydrate and potassium selenocyanate with 1,2-bis(pyridin-4-yl)ethane (bpa) in water. The FeII cation is coordinated by two N-bonded selenocyanate anions, two water molecules and two 1,2-bis(pyridin-4-yl)ethane (bpa) ligands in a slightly distorted octahedral geometry. In addition, two non-coordinating bpa molecules and two water molecules are present. The FeII cation is located on a center of inversion while the coordinating bpa ligand is located on a twofold rotation axis. The FeII cations are linked by the bpa ligands into chains along the b-axis direction, which are further connected into layers perpedicular to the c axis by O-HN and O-HO hydrogen bonds to the non-coordinating bpa and the water molecules. The crystal studied was twinned by pseudo-merohedry (180° rotation along c*; contribution of the minor twin component 3.7%).

In our recent work we have reported on the synthesis and characterization of
cobalt(II) and iron(II) selenocyanate coordination polymers that show
coexistence of metamagnetism and a slow relaxation of the magnetization
(Boeckmann & Näther, 2011; Wöhlert et al., 2012 and
Boeckmann et
al., 2012). These compounds can be prepared by thermal
decomposition of
suitable precursor compounds that contain volatile ligands like e.g.
water in hydrates and therefore, such compounds are of extreme importance for
our project. In the course of these investigations we obtained such a
precursor based on 1,2-bis(pyridin-4-yl)ethane (bpa), which was characterized
by
single-crystal X-ray diffraction.

In the crystal structure of the title compound
Fe(NCSe)2(C12H12N2)(H2O)2]n.2C12H12N2.2H2O
solvate each FeII cation is coordinated by two N-bonded
selenocyanate anions, two water molecules and two bpa ligands (Fig. 1). The
FeN4O2 octahedra are slightly distorted with distances in the range of
2.071 (4) Å to 2.344 (4) Å. The angles arround the FeII cations are in
the range of 86.91 (16) ° to 93.09 (16) ° and of 180 ° (Tab. 1). Each
FeII cation is located on a center of inversion while the coordinating
bpa ligand is located on a twofold rotation axis. The iron(II)
cations are connected by the bpa ligands into one dimensional polymeric
chains, which elongate in the direction of the crystallographic b-axis
(Fig. 2). These chains are linked by intermolecular O—H···N and O—H···O
hydrogen bonding into layers by non-coordinating bpa ligands and water
molecules perpedicular to c (Fig. 2, Tab. 2).

FeSO4×7H2O, KNCSe and 1,2-bis(pyridin-4-yl)ethane were obtained from
Alfa Aesar. All chemicals were used without further purification. 0.15 mmol
(43 mg) FeSO4×7H2O and 0.2 mmol (28 mg) KNCSe were reacted with 0.6 mmol (109 mg) 1,2-bis(pyridin-4-yl)ethane in 1 ml water. Red single-crystals of
the title compound were obtained after three days.

All H atoms were positions with idealized geometry and were refined
isotropically with Uiso(H) = 1.2 Ueq(C) using a riding model
with C—H = 0.93 Å and C—H2 = 0.97 Å. The O—H hydrogen atom were
located in a difference map, their bond lengths were set to an ideal value of
0.82 Å, and finally they were refined using a riding model with
Uiso(H) = 1.5 Ueq(O). Twinning by pseudo-merohedry of the
crystal by a 180° rotation along c* was taken into account, using a
twin matrix (-1 0 0 0 -1 0 1 0 1; BASF parameter: 0.03696) which lowered the R
value from 6.16 to 4.5%.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and
goodness of fit S are based on F2, conventional R-factors R are based
on F, with F set to zero for negative F2. The threshold expression of
F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is
not relevant to the choice of reflections for refinement. R-factors based
on F2 are statistically about twice as large as those based on F, and R-
factors based on ALL data will be even larger.